Technical Abstract:
Quorum-sensing (QS) is defined as cell-to-cell communication in response to population density in bacteria. Autoinducer-2 (AI-2)-dependent quorum-sensing has been shown to control a variety of cellular processes such as expression of virulence factors, toxin production, biofilm formation, and swarming motility in both Gram(-) and Gram(+) bacterial species. The production of AI-2 is dependent upon LuxS, the key enzyme for the final step of AI-2 biosynthesis pathway. In this study, we constructed a luxS deletion mutant in food-borne pathogen Campylobacter jejuni and confirmed that there was no AI-2 production in this mutant using the Vibrio harveyi AI-2 reporter strain BB170. The luxS mutant showed slightly slower growth rate at both 37 and 42 degree, and reduced motility at 37 degree when compared to the wild-type. The luxS mutant is also more sensitive to hydrogen peroxide and cumene hydroperoxide than wild-type. To gain a better understanding of the LuxS-controlled gene expression and the LuxS-dependent resistance to oxidative stress in C. jejuni, gene expression analyses of wild-type and luxS mutant under both hydrogen peroxide-treated and untreated conditions were carried out using DNA microarray analysis. The results showed that several operons exhibited luxS-dependent expression patterns under both conditions, including genes encoding a phosphate-transport system (pstB, pstS, pstA) and several ABC transporters, as well as genes located downstream of luxS (Cj1199, Cj1120, metE and metF). Interestingly, the expression of ahpC (encoding alkyl hydroperoxide reductase) is increased in the presence of luxS gene under hydrogen peroxide-treated condition, which is consistent with our finding that luxS mutant exhibits higher sensitivity to oxidative stress than that of the wild-type.